---
title: "Mental addition and subtraction (age 9+)"
description: "Add and subtract numbers mentally with increasingly large numbers, using place-value knowledge and derived facts"
canonical: https://lightmysky.com/learn/mathematics/mental-addition-and-subtraction-age-9-mt_MWXPiaTnEu
source: https://lightmysky.com/learn/mathematics/mental-addition-and-subtraction-age-9-mt_MWXPiaTnEu.md
retrieved: 2026-10-19
---

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# Mental addition and subtraction (age 9+)

Add and subtract numbers mentally with increasingly large numbers, using place-value knowledge and derived facts

Subject: Mathematics · Area: Addition & Subtraction · Ages 9 to 10
Page: https://lightmysky.com/learn/mathematics/mental-addition-and-subtraction-age-9-mt_MWXPiaTnEu

## Ready when they can

- Mentally calculate 45,000 + 8,000
- Mentally subtract 3,200 from 10,000 by counting up
- Use near-doubles: 2,500 + 2,600 = 5,100

## Lesson: Adding and subtracting big numbers in your head

You already know how to break numbers apart by place value and use facts you know to find new ones. Now you use those same tricks on bigger numbers, like thousands.

**Example.** Kai adds 45,000 and 8,000. He knows 45,000 is 45 thousand and 8,000 is 8 thousand. He just adds the thousands: 45 + 8 = 53. So 45,000 + 8,000 = 53,000.

*(drawing: Count up from 3,200 to 10,000: first add 800 to reach 4,000, then add 6,000 more to reach 10,000. That's 800 + 6,000 = 6,800, so 10,000 − 3,200 = 6,800.)*

**Example.** Priya adds 2,500 and 2,600. She knows the double 2,500 + 2,500 = 5,000. Since 2,600 is 100 more than 2,500, she adds that extra 100 too: 5,000 + 100 = 5,100.

**Tip.** Look for the round numbers hiding inside a big number. Breaking it into thousands, hundreds, or a double you already know makes the whole problem easier.

**Recap.** Break big numbers into place value chunks, count up to subtract, and use near-doubles to add fast in your head.

## Practice

17 questions on this page, each with its working shown.

## Needs first

- [Mentally adding tens to 3-digit numbers](https://lightmysky.com/learn/mathematics/mentally-adding-tens-to-3-digit-numbers-mt_aHQ9kNt3is)
- [Mentally adding and subtracting ones with 3-digit numbers](https://lightmysky.com/learn/mathematics/mentally-adding-and-subtracting-ones-with-3-digit-numbers-mt_oDU_8zMZjp)
- [Place Value × 10 Pattern](https://lightmysky.com/learn/mathematics/place-value-10-pattern-mt_QqG6IdmTSE)
- [Mentally adding hundreds to 3-digit numbers](https://lightmysky.com/learn/mathematics/mentally-adding-hundreds-to-3-digit-numbers-mt_xPqczp7zPX)

## Opens up

- [Adding and subtracting (age 9+)](https://lightmysky.com/learn/mathematics/adding-and-subtracting-age-9-mt_-F_Lv_apzH)
- [Mental calculation strategies](https://lightmysky.com/learn/mathematics/mental-calculation-strategies-mt_vmW2cb5c7A)